1. Field of the Invention
The present invention relates to a photo-curable resin composition and a process for preparing a mold by photo-fabrication this photo-curable resin composition.
2. Background Information
In recent years, photo-fabricating processes for forming three-dimensional objects consisting of integrally laminated cured resin layers prepared by repeating a step of forming a cured resin layer by selectively irradiating a photo-curable material with light have been proposed (see Japanese Patent Application Laid-open No. 247515/1985, U.S. Pat. No. 4,575,330 (Japanese Patent Application Laid-open No. 35966/1987), Japanese Patent Application Laid-open No. 101408/1987, Japanese Patent Application Laid-open No. 24119/1993). These photo-fabricating processes are attracting attention due to their capability of easily forming the target three-dimensional object in a short period of time even when the shape of the object is complicated.
A typical example of such a photo-fabricating process comprises forming a thin layer of a liquid photo-curable resin composition, selectively irradiating this thin layer with light using, for example, an ultraviolet radiation laser to obtain a cured resin layer, feeding the photo-curable resin composition to form another thin layer of the composition over this cured resin layer, and selectively irradiating this thin layer with light to form a new cured resin layer which is integrally laminated over the previously formed cured resin layer. This step is repeated a number of times, with or without changing the pattern in which the light is irradiated to form a three-dimensional object consisting of integrally laminated multiple cured resin layers.
The characteristics demanded of the photo-curable resin composition used for these photo-fabricating processes include a low viscosity, the capability of being rapidly cured by irradiation of light, non-swelling characteristics of the cured products when contacted by a photo-curable resin composition, and minimal deformation due to shrinkage during curing with light, such as production of warped parts, indented parts with a sink mark, or overhanging parts with curl.
Three-dimensional objects prepared by photo-fabricating methods have conventionally been used for a design model, a model for medical services, and a master model for a resin molding mold. In recent years, attempts have been made to mount parts such as a connector or a plug, and to incorporate parts for test purposes such as a heater, a motor, or an engine, directly manufactured by photo-fabricating methods. In addition to high dimensional accuracy, mechanical strength and heat resistance sufficient to withstand conditions of use are demanded of these parts. However, the conventional photo-fabricating method using a photo-curable resin composition cannot produce cured products with sufficient mechanical strength and heat resistance. It has therefore been difficult to manufacture three-dimensional objects for mounting parts and incorporating parts having good mechanical strength and heat resistance which can withstand actual conditions of use.
On the other hand, there has been an attempt to manufacture a mold used for various molding methods such as the injection molding method, press molding method, vacuum molding method, high-pressure molding method, or foaming molding method by an photo-fabrication method (such a mold made from a resin composition is hereinafter called a resin-based mold).
However, no conventional photo-fabricating method using known photo-curable resin compositions can produce photo-fabricating objects possessing sufficient pressure resistance and heat resistance as demanded of such a resin-based mold. In particular, there has been no resin composition known in the art which can produce an photo-fabricated product, such as an photo-fabricated resin-based mold, which can withstand high temperature, high pressure conditions under which engineering plastics are molded by injection. It is therefore difficult to manufacture a resin-based mold having excellent repetition durability by a photo-fabricating method.
The present invention has been achieved in view of this situation and has an object of providing a photo-curable resin composition which can produce cured products with excellent mechanical strength and heat resistance by a photo-fabricating method. Another object of the present invention is to provide a process for manufacturing a resin-based mold which exhibits high dimensional accuracy and superior repetition durability in the manufacture of molded articles.